Digital holographic interferometry with CO2 lasers and diffuse illumination applied to large space reflector metrology [Invited]

Applied Optics (Impact Factor: 1.78). 01/2013; 52(1):A102-16. DOI: 10.1364/AO.52.00A102
Source: PubMed


Digital holographic interferometry in the long-wave infrared domain has been developed by combining a CO2 laser and a microbolometer array. The long wavelength allows large deformation measurements, which are of interest in the case of large space reflectors undergoing thermal changes when in orbit. We review holography at such wavelengths and present some specific aspects related to this spectral range on our measurements. For the design of our digital holographic interferometer, we studied the possibility of illuminating specular objects by a reflective diffuser. We discuss the development of the interferometer and the results obtained on a representative space reflector, first in the laboratory and then during vacuum cryogenic test.

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Available from: Marc Georges, Mar 26, 2015
    • "We already have demonstrated various LWIR interferometric techniques like in-plane ESPI [3][4] , out-of-plane ESPI [4] and DHI [4] . Then we have presented various developments concerning large deformations metrology either in the case of space structures by LWIR DHI [5]-[7] , nondestructive testing by LWIR speckle interferometry [8]-[10] , combination of thermography and holography [11][12] and more recently vibration analysis [13][14] . "
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    ABSTRACT: We present digital holographic interferometry (DHI) in the long-wave infrared for monitoring the deformation under cryogenic conditions of a segmented focal plane array to be used in a space mission. The long wavelength was chosen for its ability to allow measurement of displacements 20 times larger than DHI in the visible and which were foreseen with the test object under such temperature changes. The specimen consists of 4x4 mosaic of detectors assembled on a frame. It was required to assess the global deformation of the ensemble, the deformation of each detector, and piston movements of each of them with respect to their neighbors. For that reason we incorporated the temporal phase unwrapping by capturing a sufficiently high number of holograms between which the phase does not suffer strong variations. At last since the specimen exhibit specular reflectivity at that wavelength, it is illuminated through a reflective diffuser.
    No preview · Article · Jan 2015 · Proceedings of SPIE - The International Society for Optical Engineering
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    • "The shaker allows vibrations up to a few tens of kHz. The blade is covered with a white powder to create scattering at that wavelength and to prevent damages on the microbolometer array by specular back reflections of the CO 2 laser [4] [5]. Figure 2(b) shows the real-time speckle interferogram with (1-J 0 ) profile for a vibration frequency of 2910 Hz. "
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    ABSTRACT: Speckle interferometry in the time-average mode at long infrared wavelengths is shown for observing the mode shapes of vibrating objects. The long wavelength allows observing larger vibration displacements than what is achieved with visible wavelengths.
    Full-text · Conference Paper · Jan 2014
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    ABSTRACT: The ability to see behind flames is a key challenge for the industrial field and particularly for the safety field. Development of new technologies to detect live people through smoke and flames in fire scenes is an extremely desirable goal since it can save human lives. The latest technologies, including equipment adopted by fire departments, use infrared bolometers for infrared digital cameras that allow users to see through smoke. However, such detectors are blinded by flame-emitted radiation. Here we show a completely different approach that makes use of lensless digital holography technology in the infrared range for successful imaging through smoke and flames. Notably, we demonstrate that digital holography with a cw laser allows the recording of dynamic human-size targets. In this work, easy detection of live, moving people is achieved through both smoke and flames, thus demonstrating the capability of digital holography at 10.6 μm.
    Full-text · Article · Mar 2013 · Optics Express
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